1. Field of the Invention
The present invention relates to changing automatic transmission fluid in automobiles, and more particularly to an apparatus and method for achieving a complete change of such fluid.
2. Description of the Prior Art
To maintain the integrity of an automatic transmission in a motor vehicle, it is necessary to periodically change the fluid. Such fluids, due to heat and pressure, deteriorate with mileage of the vehicle. Small particles of metal and the like, as the transmission wears, as well as carbon and similar substances from various materials in the transmission mix with the fluid. If fluid changes are not made at the designated periods, slippage of the transmission can occur, and eventually, the transmission fails. When fluid is drained from the transmission case at recommended periods, the used fluid will be found to be dark, indicating contaminants in the oil. Further, draining fluid by removing the transmission pan, the usual procedure, does not drain the torque converter, the transmission fluid cooler, or other areas of the transmission. It has been estimated that 50% and more of the fluid is not removed by draining only the pan. Thus, after the usual prior art method of changing the transmission fluid, a significant portion of the oil still contains contaminants, reducing the life of the transmission. It is to be noted that the volume of contaminants in a transmission will accumulate with successive fluid changes.
This problem has been recognized. U.S. Pat. No. 4,807,674 to Sweet uses a special external can with two hoses. One hose connects to a vacuum fitting on the carburetor and the other is inserted into the dip stick tube, thus using the engine vacuum to withdraw the fluid. However, no means for determining if all of the fluid has been removed is shown. Gas pressure from an external tank, and the vehicle engine, are used to remove transmission fluid in Becnel, U.S. Pat. No. 3,513,941, and the expressed fluid is caught in an open container. Brown, in U.S. Pat. No. 5,291,968 teaches a drain pan under the transmission, removal of the transmission pan and collecting the fluid for disposal. He then uses an external pump to force new fluid from a reservoir into an outlet of the transmission. The engine is then used to pump the remainder of the used fluid out as the fresh fluid is pumped in. Brown notes that simply removing the transmission pan allows only about three quarts of fluid to be drained, of the fluid capacity of twelve quarts.
Japanese patent number 2-72299 shows two tanks, interconnected by valves. An external pump connects to the oil cooler fitting and draws fluid from the transmission through the cooler and into a first tank. A solenoid valve is used to switch the pump to draw fresh fluid from a second tank and into the transmission via the oil cooler. Thus, external power must be available.
There is an unfilled need for a simple, low cost system and method that can completely change transmission fluid in a vehicle quickly and easily using the vehicle engine, and without use of external power equipment.